Today, I am a successful doctor, entrepreneur, public speaker and author. As an 18-year-old, I was a college dropout and a secretary with a five-year plan: Find a man to marry me. When the plan didn’t work, I renewed it at age 24. Note to my entrepreneurial self: Never renew a failing plan.

At 29, a disastrous relationship left me with everything I owned in a U-Haul trailer and living with my new roommates, Mom and Dad. I could have easily found another secretarial job, but I knew it was time for a major change.

I had heard, “Do what you love, and you’ll never work a day in your life.” I loved food, so I headed back to college to become a nutritionist. Three months into my education, I was feeling drawn to another field of study, but I was afraid to make another change. “What if I failed?”

I knew once I switched my major and made the announcement, there would be no turning back. When the fear of not doing it became greater than the fear of doing it, I decided to become a doctor. I worked hard for three years and graduated at the top of my class. Then, I was rejected from every medical school in the country. My dream was evaporating before my eyes.

Was the universe trying to tell me it was time to make another change? I wasn’t ready to give up on my dream, so I put myself through the yearlong application process again. I was accepted to the Mount Sinai School of Medicine -- but life had changed.

I was now 35 years old. I was also six months pregnant and still didn’t have a husband. It was daunting. I wanted to be a doctor. I wanted a baby. I didn’t know how I was going to do it, but I wasn’t willing to give anything up.

Juggling medicine and single motherhood was exhausting, but I made it through! After graduation, I chose a career as an emergency room doctor, because the shift work enabled me to schedule a life with my now 5-year-old son.

Working in the emergency room was rewarding. I saw unbelievable things, and I saved lives. But at 50, I knew it was time to move on. I walked away from that lucrative career to open a business dedicated to helping women navigate aging without surgery. I became an entrepreneur.

I had no business training and no role model. Everyone I knew went to work and collected a paycheck. No matter, I rented a space, put a $75 ad in the newspaper and sat at the reception desk myself. Today, my business, Sonas Med Spa, is unrecognizable from its humble beginnings.

When I was 63, I decided to reinvent myself again. To help others learn from my journey, I became an author. My book, Tough Cookies Don’t Crumble: Turn Set-Backs into Success, outlines the strategies that transformed me. And then at 64, I took my message on the road and became a keynote speaker.

Looking back, I realized there were underlying strategies that helped me reinvent myself time after time. If the thought of reinventing yourself is daunting -- maybe some of these strategies could help you as well.

1. Be willing to change course.

People change careers all the time -- sometimes out of choice, and sometimes because they are forced out of their comfort zone. Where you start doesn’t have to be where you end, no matter how old you are. I graduated from medical school at 39, opened a business at 50 and wrote a book at 63. The best advice I ever got came from my mother when I was feeling too old to think about medical school. “One day you’ll be 50. You’ll either be a doctor or you won’t, but you’ll still be 50. That’s your choice.” One day, you’ll be 50 or 60 or 70. You’ll either achieve your dreams, or you won’t. That’s your choice.

2. Ask for help.

People ask how I got through medical school with a baby. The answer is always the same. With a lot of help. Most of us want to help others but are often reluctant to ask for help. Many feelings get stirred up -- weakness, fear and vulnerability topping the list. But If you don’t ask, the answer will always be no. You need to ask yourself: Is getting nothing done on your own more important than completing a task with help? If not, ask for help.

3. Let your goal trump your humiliation.

Your goal needs to be more important than your feelings. No one has it together every day. Sometimes you feel vulnerable, sometimes you feel inadequate, sometimes embarrassed. Feel the feelings and keep on going.

Above all, stay focused on your goal. You don’t have to be the smartest -- you have to be the one who won’t give up. I made it through medical school with a baby and no husband, because I wouldn’t give up. Perseverance is a vital component to any success story. You can accomplish almost anything if you put your mind to it. I was a college dropout who became a doctor. Along the way, I became a warrior. Become a warrior.

More from Entrepreneur

New York Times bestselling author Nicole Lapin can help you pitch your brand to press and strengthen your media training.